U.S. patent number 7,495,366 [Application Number 11/518,977] was granted by the patent office on 2009-02-24 for compact slip ring incorporating fiber-on-tips contact technology.
This patent grant is currently assigned to Moog Inc.. Invention is credited to Michael J. Day, Norris E. Lewis, Jerry T. Perdue, Larry D. Vaught, Hettie H. Webb, Barry K. Witherspoon.
United States Patent |
7,495,366 |
Day , et al. |
February 24, 2009 |
**Please see images for:
( Certificate of Correction ) ** |
Compact slip ring incorporating fiber-on-tips contact
technology
Abstract
A compact slip ring (20), which is particularly adapted for use
in small spaces, is adapted to provide electrical contact between a
rotor (22) and a stator (21). The improved slip ring broadly
includes an electrically-conductive monofilament (24) having one
end (28) mounted on the stator and having a distal end (34); a
sleeve (25) mounted on and secured to the marginal end portion of
the monofilament, adjacent the distal end; and a fiber bundle (26)
having a longitudinal axis (39), one marginal end portion of the
fiber bundle being recessed in and secured to the sleeve, the other
end of the fiber bundle engaging the rotor such that the
longitudinal axis of the fiber bundle will be substantially
perpendicular to an imaginary line tangent to the rotor surface at
the point of contact with the longitudinal axis.
Inventors: |
Day; Michael J. (Blacksburg,
VA), Lewis; Norris E. (Christiansburg, VA), Perdue; Jerry
T. (Christiansburg, VA), Vaught; Larry D. (Pembroke,
VA), Webb; Hettie H. (Radford, VA), Witherspoon; Barry
K. (Blacksburg, VA) |
Assignee: |
Moog Inc. (East Aurora,
NY)
|
Family
ID: |
38834485 |
Appl.
No.: |
11/518,977 |
Filed: |
September 11, 2006 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20070120437 A1 |
May 31, 2007 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
10871090 |
Jun 18, 2004 |
7105983 |
|
|
|
Current U.S.
Class: |
310/232; 310/233;
310/248 |
Current CPC
Class: |
H01R
39/08 (20130101); H01R 39/24 (20130101); H01R
39/381 (20130101); H01R 39/20 (20130101) |
Current International
Class: |
H02K
41/00 (20060101) |
Field of
Search: |
;310/231-233,238,248-251,42 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lam; Thanh
Attorney, Agent or Firm: Phillips Lytle LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of U.S. patent
application Ser. No. 10/871,090, filed Jun. 18, 2004 now U.S. Pat.
No. 7,105,983.
Claims
What is claimed is:
1. A slip ring adapted to provide electrical contact between a
stator and a rotor, comprising: an electrically-conductive
monofilament having one end mounted on said stator and having a
distal end; a sleeve mounted on and secured to the marginal end
portion of said monofilament adjacent said distal end; and a fiber
bundle having a longitudinal axis, one marginal end portion of said
fiber bundle being received in and secured to said sleeve, the
other end of said fiber bundle engaging said rotor such that the
longitudinal axis of said fiber bundle will be substantially
perpendicular to an imaginary line tangent to said rotor surface at
the point of contact with said longitudinal axis.
2. A slip ring as set forth in claim 1 wherein said monofilament
has a transverse cross-section that is substantially circular.
3. A slip ring as set forth in claim 2 wherein said monofilament
has a diameter of about 0.015 inches.
4. A slip ring as set forth in claim 3 wherein said monofilament
has a spring compliance of about 0.005 inches per gram of
force.
5. A slip ring as set forth in claim 3 wherein said monofilament is
formed of beryllium copper.
6. A slip ring as set forth in claim 1 wherein said sleeve is
secured to the marginal end portion of said monofilament adjacent
said distal end by swaging, crimping or welding.
7. A slip ring as set forth in claim 1 wherein said fiber bundle
one marginal end portion is secured to said sleeve by swaging or
crimping.
8. A slip ring as set forth in claim 1 wherein said monofilament
distal end abuts one end of said fiber bundle.
9. A slip ring as set forth in claim 1 wherein there are from about
25 to about 150 individual fibers in said bundle.
10. A slip ring as set forth in claim 1 wherein the width of said
slip ring is at least about 0.040 inches.
11. A slip ring as set forth in claim 1 and further comprising a
collimator surrounding a portion of said sleeve and extending
therebeyond, the lower end of said collimator tube being adapted to
limit lateral movement of the lower marginal end portions of the
fibers in said bundle when said rotor rotates relative to said
stator.
12. A slip ring as set forth in claim 11 wherein said collimator is
formed integrally with said sleeve.
13. A slip ring as set forth in claim 1 wherein said sleeve is
configured as an elbow.
14. A slip ring as set forth in claim 1 wherein the interior
surface of said sleeve is provided with an non-oxidizing coating.
Description
TECHNICAL FIELD
The present invention relates generally to slip rings for
communicating electrical power and/or signal(s) between a rotor and
a stator, and, more particularly, to a compact slip ring that
incorporates fiber-on-tips electrical contact technology.
BACKGROUND ART
Electrical slip rings are used to transfer electrical power and/or
signal(s) between a rotor and a stator. These devices are used in
many different military and commercial applications, such as solar
array drive mechanisms, aircraft and missile guidance platforms,
undersea robots, CATSCAN systems, and the like. In some of these
applications, slip rings are used in conjunction with other rotary
components, such as torque motors, resolvers and encoders.
Electrical slip rings must be designed to be located either on the
platform axis of rotation, or be designed with an open bore which
locates the electrical contacts off-axis. Hence, the designations
"on-axis" and "off-axis" slip rings, respectively. The diameter of
slip ring motors may range from a fraction of an inch to multiple
feet, and the angular speed may vary from one revolution per day to
as much as 20,000 revolutions per minute. In all of these
applications, the electrical contacts between the rotor and stator
must: (1) transfer power and/or signal(s) without interruption at
high surface speeds, (2) have long wear life, (3) maintain low
electrical noise, and (4) be of a physical size that allows
multiple circuits to be packaged in a minimum volume.
The most efficient management of the electrical and mechanical
contact physics allows the most demanding requirements to be met.
For example, if the application is an off-axis slip ring that
allows the x-ray tube in a CATSCAN gantry to rotate about the
patient's body, the electrical contacts must be designed to carry
about 100-200 amps (with surges of hundreds of amps), operate at
surface speeds on the order of 500 inches per second, last for 100
million revolutions, and occupy a minimal volume within the gantry.
In order to meet the 100 million revolution requirement for a
device that is about six feet in diameter, the brush force must be
low to minimize frictional heating and to maintain a large number
of contact points between brush and ring to achieve the required
current density.
Four types of electrical contacts between a rotor and stator
include: (1) a composite solid material brush on a cantilevered
spring, (2) a monofilament metal alloy brush that tangentially
engages the rotor, (3) a fiber brush having a plurality of
individual fibers, with the bundle tangentially engaging the rotor,
and (4) a tip-of-fiber contact between the brush and rotor. The
contact force, surface speeds and type of lubrication for each
contact type is summarized in Table I. Table I also shows the types
of lubricants required to reduce the contact frictional heating if
the brush force is above one gram.
TABLE-US-00001 TABLE I Type of Contact Type Contact Force Surface
Speeds Lubrication composite brush 0.4 kg/cm.sup.2 700 in/sec
sacrificial graphite film* monofilament 3-20 grams 12 in/sec
boundary metal alloy lubrication** tangential fiber 1-3 grams 200
in/sec adventitious*** brush fiber-on-tip 0.1-1 grams 1200 in/sec
adventitious*** *With a sacrificial graphite film, the brush and
ring interface is lubricated by a film of graphite that is
transferred from the brush to the ring. Material that is worn away
is replaced by graphite from the brush. **With boundary
lubrication, a boundary lubricant film supports a portion of the
load between the contact members. The points of metal contact
support the remaining load between the contact members, and provide
the current-carrying capability. ***With adventitious films, very
thin films of materials that are capable of reducing the
coefficient of friction between the contact members under light
loads.
The tribological properties of electrical contacts and the right
choice of lubricant to meet the requirements of the application are
extremely important. For example, if the contacts are to be used in
a space application, then the lubricant must meet all of the
requirements of a ground based application, and have a low vapor
pressure. If the contacts have a long life requirement, then dust,
wear debris and other contaminants may accumulate in the contact
zone and create problems with life and signal transfer. However, if
the electrical contact members can be brought together with a force
of about one gram or less, then the lubricant and the associated
complications are eliminated.
For several years, fiber brushes with a tangential orientation to
the ring have been successfully used to meet high surface speeds
without the use of a lubricant.
When manufacturing slip rings in the range of four to six feet in
diameter, the costs of the ring material, as well as the costs
associated with the equipment used to cast the dielectric material
that supports the rings, the costs of equipment required to machine
the support structure, and the costs of the equipment used to
electroplate precious metal on a ring, rise dramatically if a
continuous ring approach is used. Large-diameter rings are normally
machined from plate stock or tubing of the appropriate size.
Another option is to form a metal strip of the required
cross-section, to bend it into an annulus or ring, and to weld the
facing ends together. In this case, the dimensional tolerances that
must be held for the ring I.D. and O.D. cause the continuous ring
to be prohibitively expensive. In addition, the bath required to
electrodeposit metal on a six foot diameter ring is five to six
times more expensive than that required for a 120.degree. length of
arc used to fabricate a segmented slip ring of the same
diameter.
U.S. Pat. No. 5,054,189, the aggregate disclosure of which is
hereby incorporated by reference, teaches a method of manufacturing
an annular dielectric base portion of an electrical slip ring
assembly having multiple electrical rings formed in the outer
circumference. The rings are formed from conductive metal strips of
the appropriate cross-sectional shape and configuration. When each
ring is wrapped around the circumference of the base, the facing
ends are intended to abut one another. However, because of
dimensional variations in the base O.D. and dimensional variations
in the length of the strip used to form the conductive ring, the
facing ring ends sometimes do not abut properly. In practice, the
length of the ring is controlled such that a gap always exists
between the facing ring ends. This gap may vary from about 0.020
inches to about 0.040 inches. The brush technology used with this
ring structure is the tangential fiber brush, which can readily
move over that gap without mechanical and/or electrical
interference. Over ten years of experience has shown that as the
slip ring rotates, brush and ring wear debris and other particulate
contaminants will accumulate in the gap. As the brushes continue to
move over the gap, finely divided particles are dragged onto the
ring surface, creating electrically-insulating films. Thus,
problems develop with electrical signal transmission. Millions of
ring revolutions may occur because these problems develop.
It would be generally desirable to provide an improved compact slip
ring that would allow longer life, higher current densities, and
higher rotor surface speeds to be achieved a lower costs that with
current slip ring technology, and that uses fiber-on-tips
electrical contact technology.
DISCLOSURE OF THE INVENTION
With parenthetical reference to the corresponding parts, portions
or surfaces of the disclosed embodiment, merely for purposes of
illustration and not by way of limitation, the present invention
broadly provides and improved compact slip ring that is adapted to
provide electrical contact between a stator and a rotor.
The improved slip ring (20) broadly includes: an
electrically-conductive mono-filament (24) having one end (28)
mounted on the stator (21) and having a distal end (34); a sleeve
(25) mounted on and secured to the marginal end portion of the
monofilament adjacent the distal end; and a fiber bundle (26)
having a longitudinal axis (39), one marginal end portion of the
fiber bundle being received in and secured to the sleeve, the other
end of the fiber bundle engaging the rotor such that the
longitudinal axis of the fiber bundle will be substantially
perpendicular to an imaginary line tangent to the rotor surface at
the point of contact with the longitudinal axis.
The monofilament may have a transverse cross-section that is
substantially circular, and may have a diameter of about 0.015
inches. The monofilament may have a spring compliance (i.e., the
reciprocal of the spring rate) of about 0.005 inches per gram of
force. The monofilament may be formed of beryllium copper.
The sleeve is secured to the marginal end portion of the
monofilament adjacent the distal end by swaging, crimping or
welding. The fiber bundle one marginal end portion is secured to
the sleeve by swaging or crimping. The monofilament distal end may
abut one end of the fiber bundle.
There may be from about 25 to about 150 individual fibers in the
bundle. The individual fibers may be formed of a corrosion- and
wear-resistant hand material, such as a precious metal alloy or a
suitable copper-based alloy.
The width of the slip ring (i.e., in a direction perpendicular to
the plane of the paper) may be at least about 0.040 inches.
A collimator may surround a portion of the sleeve and may extend
therebeyond. The lower end of the collimator tube is adapted to
limit lateral movement of the lower marginal end portions of the
fibers in the bundle when the rotor rotates relative to the stator.
The collimator may be formed integrally with the sleeve.
The sleeve may be configured as an elbow. The interior surface of
the sleeve is provided with a suitable non-oxidizing coating, such
as gold or a gold alloy.
Accordingly, the general object of the invention is to provide a
compact slip ring.
Another object is to provide a compact slip ring with fiber-on-tips
electrical contact technology.
These and other objects and advantages will become apparent from
the foregoing and ongoing written specification, the drawings and
the appended claims.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic view of the improved compact slip ring, this
view showing two individual slip rings as being mounted on the
stator and engaging the rotor at two different relative angular
positions.
DISCLOSURE OF THE PREFERRED EMBODIMENTS
At the outset, it should be clearly understood that like reference
numerals are intended to identify the same structural elements,
portions or surfaces consistently throughout the several drawing
figures, as such elements, portions or surfaces may be further
described or explained by the entire written specification, of
which this detailed description is an integral part. Unless
otherwise indicated, the drawings are intended to be read (e.g.,
cross-hatching, arrangement of parts, proportion,. degree, etc.)
together with the specification, and are to be considered a portion
of the entire written description of this invention. As used in the
following description, the terms "horizontal", "vertical", "left",
"right", "up" and "down", as well as adjectival and adverbial
derivatives thereof (e.g., "horizontally", "rightwardly",
"upwardly", etc.), simply refer to the orientation of the
illustrated structure as the particular drawing figure faces the
reader. Similarly, the terms "inwardly" and "outwardly" generally
refer to the orientation of a surface relative to its axis of
elongation, or axis of rotation, as appropriate.
Referring now to the drawing, and, particularly, to FIG. 1 thereof,
the present invention broadly provides an improved compact slip
ring that incorporates fiber-on-tips electrical contact
technology.
In FIG. 1, two such slip rings, severally indicated at 20, are
depicted as being operatively mounted between a stator, generally
indicated at 21, and a rotor, generally indicated at
Rotor 22 is adapted to be moved in either angular direction, as
indicated by bi-directional arrow 23.
Each slip ring is arranged to provide electrical contact between
portions of the rotor and the stator. Persons skilled in this art
will readily appreciate that the slip rings do not just communicate
the rotor with the stator. Rather, they communicated particular
circuits on the rotor with cooperative circuits on the stator so as
to establish electrical communication between these various
circuits across the rotary interface between the rotor and stator.
The two slip rings are identical, except as discussed herein, and
are illustrated as being in different angular positions relative to
the rotor. Because of this, only one of the slip rings will be
explicitly described, it being understood that the corresponding
reference numeral will refer to the corresponding part, portion or
surface of the other slip ring.
As noted at the outset, the invention provides a compact slip ring,
it is adapted for use where the physical spacing between the rotor
and stator is relatively small. In prior application Ser. No.
10/871,090, the disclosed forms of the slip ring were particularly
adapted for use with large-diameter rotors, such as used in CATSCAN
machines, and the like. The foregoing statement is not intended to
be limitative of the scope of the claims in the earlier
application. However, by way of contrast, the present invention is
particularly suited for use where the spacing between the rotor and
stator is more limited. Hence, the present invention is regarded as
being a compact slip ring. Here again, while this is preferred,
this statement should not be regarded as being limitative of the
scope of the appended claims.
Adverting now to FIG. 1, the improved slip ring is shown as broadly
including an electrically-conductive monofilament fiber, generally
indicated at 24; a sleeve 25; and a fiber bundle, generally
indicated at 26.
The monofilament 24 is formed of a suitable electrically-conductive
material, such as beryllium copper. In the preferred embodiment,
the monofilament has a substantially circular transverse
cross-section of a diameter of about 0.015 inches. However, while
is illustrative of the preferred embodiment, it should be clearly
understood that the monofilament may have other transverse
cross-sectional shapes as well. For example, the monofilament may
have a square, rectangular, polygonal, oval, or some other
transverse cross-sectional shape or configuration.
In the illustrated form, the monofilament is an integrally-formed
element bent to have a somewhat S-shape or appearance. More
particularly, the monofilament has one marginal end 28 secured to
the stator so as to be electrically conductive therewith, has one
marginal end portion 29 extending downwardly therefrom, has a bend
30, has an intermediate portion 31, has a second bend 32, and has a
distal marginal end portion 33 terminating in a circular end face
34. Ideally, the monofilament may be formed suitably bending the
monofilament to the shape shown. In the embodiment shown to the
left in FIG. 1, the arcuate portions 30 and 32 nominally inscribe
angles of about 90.degree.. In the embodiment to the right in FIG.
1, the monofilament is shown as having moved toward the rotor so as
to maintain contact therewith. In other words, whereas angled
portion 32 in the right embodiment is still about 90.degree.,
angled portion 30 now encompasses an obtuse angle of greater than
90.degree..
The slip ring may be formed of a suitable material such as
beryllium copper, and typically has a spring compliance on the
order of about 0.005 inches per gram of force. As used herein,
spring compliance is the reciprocal of the spring rate. Persons
skilled in this art will readily appreciate that the equation for
the force of a spring is F=kx, where F is the Force, k is the
spring rate and x is the displacement. As used herein, the term
"spring compliance" is 1/k.
Adverting now to the drawing figure, the sleeve 25 is mounted on
and secured to the marginal end portion of the monofilament
adjacent its distal end 34. More particularly, in the form shown,
the sleeve is configured somewhat as an elbow. The sleeve is formed
of a suitable conductive material, and one or more surfaces thereof
may be plated with a non-oxidizing material, such as gold. The
upper marginal end portion of the sleeve is suitably secured, as by
swaging, crimping or welding, to the distal marginal end portion of
the mono-filament. In the drawing figures, the upper marginal end
portion of the tube is shown as having an annular indentation,
indicated at 35, that results from a swaging or crimping operation.
Alternatively, the sleeve could be suitably welded, such as
electronically or ultrasonically, to the sleeve.
The other end of the sleeve is shown as receiving a bundle 26 of
individual fibers. The upper end face of these fibers are shown as
abutting the distal end face 34 of the monofilaments so as to be in
the electrical contact therewith. As indicated, the upper marginal
end portion of the fiber bundle is received in the lower open end
of the sleeve. The sleeve may be suitably deformed, as be crimping
or swaging, to hold the fiber bundle in this position. In the
drawing figure, the sleeve is shown as having an annular
indentation 36 which results from this crimping or swaging
operation. The lower operation end portion of the fibers extends
downwardly beyond the lower end face 38 of the sleeve, and is in
continuous touching contact with the outer surface of the rotor.
More particularly, the nominal center line 39 of the fiber bundle
is maintained so as to be substantially perpendicular to an
imaginary line (not shown) tangent to the point of contact. Thus,
with the improved actuator, the tips of the individual fibers are
held in touching contact with the outer surface of the rotor. The
fiber bundle may have from about 25 to about 150 individual
fibers.
The illustrated embodiments do differ in that the embodiment to the
right is shown as having an integrally-formed collimator portion 40
that extends downwardly below the nominal end face of the leftward
sleeve. The purpose of this collimator is to limit lateral movement
of the lower marginal end portions of the fibers in the bundle when
the rotor rotates relative to the stator. In the preferred form,
this collimator is formed integrally with the sleeve. However, this
is not invariable.
Therefore, the present invention broadly provides an improved slip
ring, which is particularly adapted for use in compact spaces, that
is adapted to provide electrical contact between a rotor and a
stator. The improved slip ring broadly includes an
electrically-conductive monofilament having one end mounted on the
stator and having a distal end; a sleeve mounted on and secured to
the marginal end portion of the monofilament, adjacent the distal
end; and a fiber bundle having a longitudinal axis, one marginal
end portion of the fiber bundle being recessed in and secured to
the sleeve, the other end of the fiber bundle engaging the rotor
such that the longitudinal axis of the fiber bundle will be
substantially perpendicular to an imaginary line tangent to the
rotor surface at the point of contact with the longitudinal
axis.
Modifications
The present invention contemplates that many changes and
modifications may be made. For example, the relative size and
diameter of the rotor is not deemed to be particularly critical,
although the invention is particularly suited for use in a compact
space.
The manner of attachment or securement of the monofilament to the
stator is not deemed critical, and may be varied while the
monofilament should be formed of an electrically-conductive
material. While beryllium copper is one such material, other types
of electrically-conductive materials might be substituted
therefore. As previously indicated, the transverse cross-section of
the monofilament. Similarly, the monofilament may be bent or
otherwise configured to have shaped other than that specifically
illustrated in the drawing.
The sleeve may be bent to the form of an elbow or may have some
other shape as well. The upper marginal end portion of the fiber
bundle is preferably received in the open mouth of the sleeve, and
is suitably secured therein, as by crimping or swaging. Similarly,
it is presently preferred that the sleeve be crimped, swaged or
welded to the monofilament.
The rotor may be in the form of a cylinder (as shown), or may be of
the pancake type. See, e.g., U.S. Pat. Nos. 5,901,429 and 6,222,297
for examples of pancake-type rotors.
Therefore, while the presently-preferred forms of the improved slip
ring have been shown and described, and several modifications
thereof discussed, persons skilled in this art will readily
appreciate that various additional changes and modifications may be
made without departing from the spirit of the invention, as defined
and differentiated by the following claims.
* * * * *